Neuralink will probably fail in interesting and worthwhile ways.

The chip

This is perhaps the most intriguing part of the Neuralink effort. According to Neuralink's DJ Seo, the company is iterating chip designs at a three-month pace and has brought the size down by a factor of seven over multiple generations. The design Neuralink is currently testing has a number of components, but the most interesting of those are the components that take input from the electrodes.

Neural signals are both analog and extremely noisy. But in the systems we've looked at so far, information is carried by what are called "spikes." These involve a dramatic change in voltage that quickly returns to background levels.

Neuralink's chip is designed to take the raw input from its electrodes, filter out some of the noise, and then identify the spikes. It then registers the spikes in an extremely compact data format (Seo said compression is about 200-fold) and sends it along to the controller sitting outside the skull. Right now, the chip uses a USB-C connection for data transfer, but it's intended to handle communication and receive power wirelessly. It can apparently get enough power that way to stimulate 64 electrodes at once, and it can switch targets to stimulate additional ones.

An evolution

A lot of Neuralink's vision may sound difficult to believe, but the company's roadmap, in many ways, starts as an extension of existing work. We have surgically implanted electrodes in both humans and animal subjects, and we have successfully read neural activity. In some cases, we've even used those readings to perform tasks, like controlling a mouse cursor or even a robotic arm, as in the video below. But there appear to be a number of key advances in what Neuralink is working on, one obvious, the others less so.

Note the word choice: "appear" is needed because it wasn't always clear what's ready for use and what, in the words of Neuralink scientist Phil Sabes, is "aspirational." (Some of the clearly aspirational ideas were well into the realm of science fiction; we'll come back to those in a bit.)

There has been some astonishing progress with BCI work.

The obvious Neuralink advance is the size of the implant. As you could see in that video, existing electrodes are hooked up to a substantial box that protrudes from the skull, needed in part because the electrodes need adaptors before they can talk to any other hardware. Neuralink wants to get rid of all of that. It wants the surgery to be elective and outpatient, and it wants the recipients of its hardware to be able to go home with it and go about their lives as normal. In service of that goal, the company has gotten rid of most of this complexity, reducing the implant to electrodes directly integrated into a small chip on a circuit board with a USB-C connection.

The chip, and the fact that it is integrated with its electrodes, is the key to this advance. While there has been some hardware demonstrated in academic labs that allows mice and rats to move freely with implanted electrodes, that hardware's still quite a bit bulkier, and the animals are undoubtedly aware of its presence. If Neuralink gets its wireless connection working, the results would be somewhat better than the cutting edge present in research labs, and made in volume.

Research animals have been getting ever-smaller implants, although the smaller implants haven't shifted to humans yet.

This is where the research community was heading, but Neuralink should get the community there with the consistency of hardware that's produced at scale. And the Neuralink scientists made it clear they want to cooperate with researchers when the hardware's ready. (When talking about using this in animal research, Musk joked, "We even care about rats, even though they carry the Black Death.")

But Neuralink wants its hardware to be approved for use in humans, where it would represent a much more dramatic advance. Use in humans, however, will require extensive testing of everything. The safety of the electrodes and their lifespan within the brain environment, the surgical robot and implantation process, and the chip itself (which is meant to be implanted under the skull) will all need extensive validation. Assuming everything passes, however, Neuralink could dramatically lower the complexity of placing implants in humans, as well as the impact of having an implant on the patient's day-to-day existence.

What's less clearly an advance is the data coming out of this system. From the images shown during Neuralink's presentations, the raw data is relatively noisy, and it seems to have a lot of drift where the entire pattern of neural activity shifts up and down somewhat. I don't think that the noise is enough to keep the processor from identifying clear spikes in the activity of the neurons it's monitoring, but I'm less certain any borderline activity will stand out enough to register. This is something that may have to be sorted out through trial and error.

Enlarge/ One day, Neuralink hopes implantees will be sent home with an app on their phone that monitors the device and lets them control it.

Revolution or science fiction?

Overall, if things work as they're expected to, the system currently in development by Neuralink represents a significant advance over existing brain-computer interfaces. At over 1,000 electrodes in a compact format, there are plenty of existing use cases, both in humans and in animal research, that could benefit from something like a near-future iteration of this hardware.

But Musk and the Neuralink execs aren't interested in existing use cases. Their goal is to make this so simple to implant that it can be done on an outpatient basis. Implantees would be sent home with an app on their phone that monitors the device and lets them control it.

That's the sort of game-changing technology that Musk has been drawn to in the past, but the brain is a radically different engineering problem than rockets or cars. This is not something where rapid iteration and learning through failure are necessarily going to work. Musk seemed to have accepted this, acknowledging how hard the work will be and that it will take longer than he'd like. That's a good attitude to have, as some of the ideas floated during Neuralink's announcement are going to be extremely challenging.

To begin with, we have little experience with having electrodes like these reside deep in the brain for decades; we simply haven't been doing this sort of work for long enough for that to be possible. And, while the scarring caused by early attempts seems to have been sorted out, we really don't know if a set of electrodes will be able to consistently listen to and stimulate the same neurons 30 years after they're implanted. This issue is compounded by the fact that Neuralink is talking about implanting multiple devices—Musk said they think that as many as 10 would be safe, but Neuralink will probably limit things to "only" five.

Enlarge/ Neuralink's intro had some features that looked more like an Apple product launch.

John Timmer

Why would you need more than one implant? Because some of the things Musk is talking about will require talking with different parts of the brain. For example, he mentioned giving an artificial limb haptic feedback, an excellent goal. But controlling the limb would require a connection to the motor cortex, while the feedback would have to be fed in to the sensory processing system. These are in distinct areas of the brain and would therefore require separate sets of electrodes to communicate with.

There's no reason in principle this couldn't be done, but it hasn't yet been tried. In part, that's because any one implant creates the risk of damage to neurons, the connections among them, and the tissues that support them. Each additional implant would increase that risk. Obviously, the risk is typically low enough that implants are often considered a reasonable option for people, but nonetheless the risk definitely exists. Adding additional implants and targeting multiple brain regions will undoubtedly increase it.

As we mentioned in our earlier analysis of Neuralink, there's also the coding problem. For any of this to work, we have to understand how the information transmitted by neurons is encoded. This will vary among different regions of the brain; a set of signals traveling along the optical nerve won't mean the same thing as an identical set of signals flowing around the hippocampus as it tries to dredge up a memory.

Further Reading

Even when implants target the same brain region, there's going to be variation from implant to implant and patient to patient. That's because a given brain region contains a large population of neurons that often do distinct or partially overlapping of things. For example, in the visual cortex, some groups of cells will register the presence of vertical features; others horizontal ones; still others pick up motion; and so on. Each set of electrodes will pick up signals from different subsets of these populations, meaning each individual's system will have to learn to understand the particular intricacies of the brain activity it's listening in on. Sending signals back will probably require learning by both the implant controller and the person implanted.

Aiming for science fiction can find (science) fact

None of these challenges is insurmountable. But they're all real, and they're what stands between an obvious extension of existing technology and Musk's mid-term vision. That vision is currently in the science fiction realm: multiple implants, put in place through elective outpatient surgery, communicating wirelessly with a small bit of hardware behind the ear, and it's all controlled by a cellular phone. No individual part of that vision is too far beyond existing technology, but assuming that all of these individual challenges can be overcome (or at least overcome in a specific, convenient manner) is extraordinarily optimistic.

Obviously anything beyond that is clearly in the realm of science fiction, much like the whole idea motivating this: Musk's hope is that getting humanity integrated into computers' home turf might make AI less hostile.

But that's not to say that this is going to be a wasted effort, even if none of these visions come to pass. Based on the development of most technologies, the people at Neuralink will struggle to get their preferred solutions to all these challenges to work. Yet there's a reasonable chance that they'll get something to work and end up solving somewhat different problems in the process. And it's exactly because they've chosen to tackle an incredibly interesting set of challenges that whatever they do end up solving could be pretty consequential.